The present invention relates a control of an engine in a xe2x80x9cdrive-by-wirexe2x80x9d vehicle, and more particularly, to a control of engine output torque in response to driver demand, cruise control, and traction control inputs.
Vehicles referred to as xe2x80x9cdrive-by-wirexe2x80x9d are the type having no mechanical connection between the accelerator pedal and the throttle valve. Those vehicles are typically equipped with a pedal position sensor whose output is translated into desired engine output torque, and wherein an engine throttle valve is opened a corresponding amount by a motor to achieve the desired engine output torque.
Further, some vehicles are equipped with cruise control systems that automatically control throttle valve opening to maintain the vehicle at a substantially constant speed selected by the driver even when the accelerator pedal is not depressed. Some are also equipped with traction control systems that determine desired engine output torque based on the amount of slip of the wheels of the vehicle in order to improve vehicle performance regardless of road conditions. The need, however, exists for controlling the throttle opening, and therefore engine output torque, by arbitrating between driver demand, cruise control system demand, and traction control system demand. In accordance with a conventional method as described in U.S. Pat. No. 5,400,865, three different target opening angles of the throttle valve are calculated based on driver input, cruise control system demand and traction control system demand. The system chooses one of the three target opening angles to calculate desired engine output torque based on a selected mode of operation. For example, traction control request is selected if the vehicle is in the traction control mode, and the desired throttle opening angle requested by the traction control system is smaller than one or both target opening angles requested by the driver or the cruise control system. If the system is not in a traction control mode, cruise control demand overrides driver demand.
The inventors herein have recognized a disadvantage with the above approach. Namely, on flat or slightly uphill slopes, the driver will not detect a response to pedal depression until the driver requested throttle opening angle exceeds the cruise control requested throttle opening angle, resulting in delayed vehicle response to driver command. Also, on downhill slopes, when the cruise control is engaged and the driver depresses the pedal to accelerate the vehicle, the vehicle response may not be as smooth as desirable.
An object of the present invention is to provide improved engine output torque control by improving interaction between two or more of the driver demand, cruise control system and traction control system. The above object is achieved and disadvantages of prior approaches overcome by a method for controlling an engine in a vehicle equipped with a constant speed control system, the method consisting of: reading a pedal position sensor output; adjusting said pedal position sensor output when the constant speed control system is engaged; calculating a first target engine output torque based on said adjusted pedal position sensor output; calculating a second target engine output torque based on an operating condition; calculating a desired engine output torque based on said first target engine output torque and said second target engine output torque; and controlling an engine parameter to achieve said desired engine output torque.
In another aspect of the present invention, the above object is achieved and disadvantages of prior approaches overcome by a method for controlling an engine in a vehicle equipped with a cruise control system and a traction control system, the method consisting of: reading a cruise control system output; calculating a first target engine output torque based on said cruise control system output; calculating a second target engine output torque based on an engine operating condition; calculating a third target engine output torque based on a traction control system output; setting a desired engine output torque to be equal to the lesser of said third target engine output torque and a sum of said first target engine output torque and said second target engine output torque; and controlling an engine parameter to achieve said desired engine output torque.
In yet another aspect of the present invention, the above object is achieved and disadvantages of prior approaches overcome by a method for use with an internal combustion engine in an engine coupled to a cruise control system, the method consisting of: calculating a target engine output torque based on an input from the cruise control system; reading a pedal position sensor output; calculating an engine output torque adjustment value based on said pedal position sensor output and on an engine operating condition; and controlling an engine parameter to adjust said target engine output torque based on said calculated engine output torque adjustment value.
An advantage of the above aspects of the present invention is that more precise engine output torque control can be achieved by improving the interaction between the driver demand, cruise control and traction control systems. In accordance with the present invention, if the driver initializes the cruise control and then tips-in from any point of the pedal position, the system will react immediately and smoothly by increasing engine output torque gradually by an incremental value proportional to the pedal position. This will eliminate delayed vehicle response on flat or slightly uphill slopes and will also provide smooth vehicle performance on downhill slopes. This method will therefore improve drive feel and will result in greater driver satisfaction with the vehicle.